1. Field of the Invention
This invention relates generally to picture processing and, in particular, to a technique for extracting features called "strokes" with predefined characteristics from images.
2. Description of the Prior Art
When a machine, such as a computer, is required to "intelligently" process an image, the image must first be converted into an internal representation with which the machine can deal effectively. The conversion is necessary to reduce the very large amount of information which represents the image to a more manageable size, and generally involves specifying the picture attributes in terms of one or more features each having predefined characteristics. Typically, the internal representation is orders of magnitude more compact than the original image, advantageously reducing the time and space required for the machine to process the image. Examples of the features used to represent attributes of a picture include descriptions and plans of its edges, skeletons and regions. Another feature of interest is called a stroke, which is defined herein to include a rectangular area in the picture having a uniform visual characteristic (e.g. intensity). Strokes are useful in many picture processing tasks, including optical character recognition.
Known techniques for reducing images to internal forms by extraction of features such as strokes are generally slow, since the large amount of information describing the individual elements of the picture must be processed one by one, in a predetermined sequence. Most processing techniques are "data directed", requiring a memory to store a large amount of state information which specifies previous test results. In addition, while some special purpose hardware has been designed to improve the feature extraction process by parallel processing, complex algorithms are often necessary to enable processing using general purpose hardware.
In view of the foregoing, it is the broad object of the present invention to enable extraction of features with predefined characteristics, particularly strokes, from an image using special purpose hardware and a processing algorithm that is efficient and easy to implement.